It is known to provide a controller for controlling an amount of power developed by a powertrain of a vehicle. Known controllers receive a signal from an accelerator pedal of the vehicle indicating the position of the pedal with respect to an allowable range of travel of the pedal. The controller controls the powertrain to develop an amount of torque that is calculated from a map of powertrain torque as a function of accelerator pedal position and other data such as potentially available torque and engine speed.
It is also known to provide a vehicle having a control system that is operable in one or more of a plurality of driving modes which may also be referred to as control modes or operating modes. In each driving mode, the control system is configured to cause each one of a plurality of vehicle subsystems to be operated in a subsystem configuration mode appropriate to the driving condition.
In one known system the subsystems include an engine management system, a transmission system, a steering system, a brakes system and a suspension system. The engine management system is configured to control the amount of torque developed by an engine of the vehicle in dependence on the position of an accelerator pedal of the vehicle. In order to do this the engine management systems refers to a map of required engine torque as a function of accelerator pedal position that is stored in a memory of the controller. The engine management system stores a plurality of maps and associates one map with each configuration mode of the engine management system. The map associated with each configuration mode is adapted to provide improved vehicle performance.
The control modes typically include a grass/gravel/snow control mode (GGS mode) that is suitable for when the vehicle is travelling in grass, gravel or snow terrain, a mud/ruts control mode (MR mode) which is suitable for when the vehicle is travelling in mud and ruts terrain, a rock crawl/boulder mode (RB mode) which is suitable for when the vehicle is travelling in rock or boulder terrain, a sand mode which is suitable for when the vehicle is travelling in sand terrain (or deep soft snow) and a special programs OFF mode (SP OFF mode or SPO mode) which is a suitable compromise mode, or general mode, for all terrain conditions and especially vehicle travel on motorways and regular roadways. A number of control modes, and examples of their implementation, are disclosed in US2003/0200016, the content of which is hereby incorporated by reference.
The different terrain types are grouped according to characteristics of the terrain (such as surface friction and roughness). For example, it is appropriate to group grass, gravel and snow together as terrains that provide a low friction, smooth surface and it is appropriate to group rock and boulder terrains together as high friction, very high roughness terrains. Low friction modes may also include an ice mode in which the subsystems are controlled in a manner suitable for driving on ice, and one of which may be a mud mode in which the subsystems are controlled in a manner suitable for driving on mud.
In the GGS control mode, the engine management system employs an accelerator pedal position/engine torque map that provides relatively low levels of engine torque during an initial range of positions of the accelerator pedal, the amount of torque increasing more rapidly as a function of pedal position over a middle range of positions between an undepressed pedal position and fully depressed pedal position. The relatively low levels of engine torque during the initial range of positions is advantageous in reducing excessive wheel spin when a driver attempts to accelerate a vehicle from rest.
In contrast, in the RB mode, the engine management system employs an accelerator pedal position/engine torque map that provides a relatively abrupt increase in engine torque during an initial range of positions of the accelerator pedal, in order to facilitate climbing of rocks and other obstacles presenting a relatively abrupt, steep increase in gradient of a path of travel of a vehicle.
As noted above, in the sand mode the subsystems are controlled in a manner suitable for driving on sand. A traction control system may be arranged, when the control system is in the sand mode, to allow only relatively low levels of wheel spin when the vehicle is traveling at low speeds so as to avoid the vehicle wheels becoming submerged in sand, but to allow relatively high levels of wheel spin when the vehicle is traveling at higher speeds. In the sand mode, the engine management system is arranged to provide relatively low levels of drive torque for a given accelerator pedal position at low vehicle speeds and to provide relatively high levels of drive torque for a given throttle pedal position at higher vehicle speeds.
It is an aim of the present invention to provide improved traction characteristics for a motor vehicle when driving in conditions where surface coefficient of friction between one or more wheels of a vehicle and a driving surface is relatively low.